An electrosurgical unit for achieving coagulation of tissue during endoscopic surgery, comprising: an endoscope having a plurality of working channels, each channel having a predetermined diameter, a flexible, hollow tube disposed in one of the working channels of the endoscope, having a diameter which is less than the diameter of the channel through which it is inserted. The tube is positioned within the working channel such that a portion of the tube including the opening at its distal end protrudes beyond the opening at the distal end of the endoscope and the tube is aligned such that a gas stream exiting from the opening at the distal end of the tube is directed onto an area to be coagulated.; An electrode is positioned inside the tube for ionizing the inert gas, the electrode being offset from the opening at the distal end of the tube a minimum safety distance, in such manner that the electrode cannot come into contact with the tissue. A source of pressurized, ionizable inert gas is connected to the opening at the proximal end of the tube and pressurized such that a stream of gas flows from the source, exits through the tube through the opening at the distal end of the tube, the longitudinal axis of the portion of the tube that protrudes from the endoscope being positioned generally parallel to an area of tissue to be coagulated to achieve coagulation, and means for adjusting a first and a second flow rate during coagulation for standby Operation and to the exit opening of the tube.; Markers are positioned on the distal end of the tube in order to allow the observation the protrusion of the tube out of the working channel.